Mike Simpson has been atop the Tea Party hit list for much of this election year.

And Tuesday's primary contest between the Idaho Republican congressman and Tea Party challenger Bryan Smith had been billed as a big one in a string of GOP primary mashups that would signal the sway of the Tea Party faction — or the ability of traditional conservatives like Simpson to fight back in a deep red state.

In the campaign's waning days, however, internal polls suggest that Simpson, who according to most recent finance reports has raised $1.9 million to Smith's $781,425, appears on track to beat back his Tea Party challenger after a campaign swamped with outside money.

While Simpson has a solid 80-plus rating from the American Conservative Union, he ran afoul of the Tea Party by voting for the 2008 Wall Street bailout. It doesn't help that he's a close ally of a face of the GOP establishment, House Speaker John Boehner.

In hisdeep-red eastern Idaho district, the only real danger for Simpson is in the primary. And there he has shown some weakness: In 2010, he won 58 percent in the GOP primary, a relatively low percentage for an incumbent. (In 2012, Simpson bounced back by winning 70 percent against a Tea Party challenger.)

All of that made him an early target of the D.C.-based Club for Growth, a small-government and free-market-oriented group which moved aggressively to help bankroll Smith, a lawyer and debt collector.

Outside Money, Divided Party

The campaign has been peppered with fierce attack ads, including those from both sides that starred one of the GOP's most enduring villains, House Minority Speaker Nancy Pelosi.

"Mike Simpson is a very energized candidate right now and is working his tail off," says Patrick Sullivan, a Republican lobbyist and campaign consultant based in Idaho, where in 2010 Tea Party activists took control of the state Republican Party.

"Establishment Republicans — I call them traditional Republicans — are starting to reactivate, to take the GOP back," Sullivan, a Simpson backer, says. "The Club for Growth may have come storming into town, but I think people are really tired of D.C. money coming in."

The D.C. money is flowing on both sides — the U.S. Chamber of Commerce is among outside groups that have invested heavily in Simpson's campaign.

Adding intrigue to the race is the deep divide in Idaho's Republican Party, a rift that has developed since Tea Party activists took control of its apparatus. They have been warring with mainstream conservatives over Tea Party opposition to the establishment of the state's health insurance exchange, and over aspects of a party platform adopted in 2012 that calls for repeal of the Constitution's provision for the direct election of U.S. senators, the end of the Federal Reserve, and "sovereignty" for the state.

"We're a conservative state, and the Tea Party that used to be talking about cutting taxes has now has moved into an anarchist movement," says Sullivan.

Trade and business groups, including the U.S. Chamber, have poured money into Simpson's reelection bid. Opensecrets.org reports that the chamber invested about $600,000 in the incumbent's effort. It also reported that Club for Growth Action, the group's super PAC, spent nearly $480,000 attacking Simpson.

Recent reports suggest, however, that the club has stopped spending in Idaho, and moved its resources to Nebraska, where earlier this week a Senate candidate it supported, Ben Sasse, won a GOP primary.

"We did move considerable resources into the Nebraska Senate race in the last two weeks," says Barney Keller of the Club for Growth. "We're in a constant state of assessing and re-assessing our races, moving resources in and out — depends on the day or week."

Idaho's biggest business lobby has also been involved in the race, on behalf of Simpson, and specifically to push back on the Club's efforts.

"Clearly the business community has stepped up and been involved," says Alex LaBeau, president of the Idaho Association of Commerce and Industry. "We are working together to make sure the Club for Growth won't be successful in the state of Idaho.

"They have overestimated their ability to send an incorrect message to voters in the state of Idaho," says LaBeau, asserting that state party organizations have "become more about sticking to an ideology than doing what their job should be, electing candidates."

Outside groups supporting Simpson, including the GOP superPAC Defending Main Street, have aired critical ads about the influence of Tea Party-affiliated outside groups, as well as Smith's work as a personal injury lawyer and debt collector. The Club for Growth has run ads attempting to link Simpson to Pelosi, and hammering him for his bailout vote.

Pushback To 'Wild Right'

The state's other congressman, two-term Tea Party Republican Raul Labrador — who last year was one of a dozen GOP House members who refused to support Boehner for speaker — has backed Smith and endorsed Republican Gov. "Butch" Otter's Tea Party challenger.

In a district with one of the heaviest concentrations of Mormons in the nation, Mitt Romney, the GOP's 2012 presidential nominee, has campaigned for Simpson, saying he wants to prevent voters from veering "wild right."

"It's all a matter of turnout," says Smyser, the conservative Boise lobbyist. "You can count on the Tea Party Republicans voting in a higher number than the Main Street or business Republicans.

"If we get 28 percent of registered voters out, I think you'll see Simpson and Otter win big," he says.

How Simpson fares against this year's Tea Party challenge won't be the only thing Idaho Republicans will be watching Tuesday: The local GOP precinct committee races are also being decided.

The winners of those parochial contests will represent their area party members at the state Republican Party's June convention, and will determine the direction of the party.

"There is a battle going on at the precinct level that we haven't seen in my memory," says Smyser, a fifth-generation Idaho resident. "It is a battle for the soul of the party."

Update on Sunday, May 18 at 11:30 a.m. ET.

After this story was published, a spokesman for Labrador on Sunday reiterated that the congressman has not endorsed Smith, and asserted that he has remained neutral in the race.